Sunroof rattle only when in ventilation position

I'm experiencing  Superb 2014 sunroof rattle, which occurs only when sunroof is in ventilation position.

There is no rattle when sunroof is closed or fully open. 

I've complained this to the dealer but they said there's nothing much to do (except for changing the sunroof, which of course is ridiculously expensive).

It's not a mayor issue but still... have anyone had similar problem with some reasonable fix?

I've attached video containing rattling sound. 

It seems to come from the front side of sunroof.